I have both an applehead & a deerhead Chihuahua, both one year old, but not brothers. There is a distinct difference in both temperament & size/shape, except.....they seem to be the exact opposites of what you describe above. My deerhead (Paco) has all the regular physical characteristics, taller, leaner, longer snout, etc. & my applehead (Diego) has the characteristics typical to the standard, BUT their temperaments are the opposite of what you describe. The applehead is *very* outgoing, loving & friendly to everyone & the dearhead is very shy & even growls at people who try to pet him. He's only friendly to me & even then, less so that the applehead.